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Cumulus Linux

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If you are using the current version of Cumulus Linux, the content on this page may not be up to date. The current version of the documentation is available here. If you are redirected to the main page of the user guide, then this page may have been renamed; please search for it there.

What Just Happened (WJH)

What Just Happened (WJH) provides real time visibility into network problems and has two components:

  • The WJH agent enables you to stream detailed and contextual telemetry for off-switch analysis with tools, such as NVIDIA NetQ.
  • The WJH service enables you to diagnose network problems by looking at dropped packets. WJH monitors forwarding (layer 2, layer 3, and tunnel) related issues.

Enable the WJH Service

Cumulus Linux does not enable the WJH service by default. To enable the WJH service:

cumulus@switch:~$ sudo systemctl enable what-just-happened
cumulus@switch:~$ sudo systemctl start what-just-happened

Run WJH Commands

After you start the WJH service, you can run the following commands from the command line.

Command
 Description
what-just-happened poll Shows information about dropped packets due to forwarding-related issues (layer 2, layer 3, and tunnel only). The output includes the reason for the drop and the recommended action to take.

The what-just-happened poll forwarding command shows the same information.
what-just-happened poll --aggregate Shows information about dropped packets due to forwarding-related issues aggregated by the reason for the drop. This command also shows the number of times the dropped packet occurs.

The what-just-happened poll forwarding --aggregate command shows the same information.
what-just-happened poll --export Saves information about dropped packets due to forwarding-related issues into a file in PCAP format.

The what-just-happened poll forwarding --export command shows the same information.
what-just-happened poll --export --no_metadata Saves information about dropped packets due to forwarding-related issues into a file in PCAP format without metadata.

The what-just-happened poll forwarding --export --no_metadata command shows the same information.
what-just-happened dump Displays all diagnostic information on the command line.

Run the what-just-happened -h command to see all the WJH command options. (WJH only supports the forwarding channel.)

Command Examples

The following example shows all dropped packets and the reason for the drop:

root@switch:~# what-just-happened poll
#    Timestamp              sPort  dPort  VLAN  sMAC               dMAC               EthType  Src IP:Port  Dst IP:Port  IP Proto  Drop   Severity  Drop reason - Recommended action
                                                                                                                                   Group
---- ---------------------- ------ ------ ----- ------------------ ------------------ -------- ------------ ------------ --------- ------ --------- -----------------------------------------------
1    21/06/16 12:02:42.052  swp1   N/A    N/A   44:38:39:00:a4:84  44:38:39:00:a4:84  IPv4     N/A          N/A          N/A       L2     Error     Source MAC equals destination MAC - Bad packet was received from peer
2    21/06/16 12:02:42.052  swp1   N/A    N/A   44:38:39:00:a4:84  44:38:39:00:a4:84  IPv4     N/A          N/A          N/A       L2     Error     Source MAC equals destination MAC - Bad packet was received from peer
3    21/06/16 12:02:42.052  swp1   N/A    N/A   44:38:39:00:a4:84  44:38:39:00:a4:84  IPv4     N/A          N/A          N/A       L2     Error     Source MAC equals destination MAC - Bad packet was received from peer
4    21/06/16 12:02:42.069  swp1   N/A    N/A   44:38:39:00:a4:84  44:38:39:00:a4:84  IPv4     N/A          N/A          N/A       L2     Error     Source MAC equals destination MAC - Bad packet was received from peer

The following example shows that packets drop five times because the source MAC address equals the destination MAC address:

root@switch:~# what-just-happened poll --aggregate
Sample Window : 2021/06/16 12:57:23.046 - 2021/06/16 14:46:17.701

#  sPort  VLAN  sMAC               dMAC               EthType  Src IP:Port  Dst IP:Port  IP Proto  Count  Severity  Drop reason - Recommended action
-- ------ ----- ------------------ ------------------ -------- ------------ ------------ --------- ------ --------- -----------------------------------------------
1  swp4   N/A   44:38:39:00:a4:87  44:38:39:00:a4:87  IPv4     0.0.0.0:0    0.0.0.0:0    ip        100    Error     Source MAC equals destination MAC - Bad packet was received from peer
2  swp1   N/A   44:38:39:00:a4:80  44:38:39:00:a4:80  IPv4     0.0.0.0:0    0.0.0.0:0    ip        100    Error     Source MAC equals destination MAC - Bad packet was received from peer

The following command saves dropped packets to a file in PCAP format

root@switch:~# what-just-happened poll --export
PCAP file path : /var/log/mellanox/wjh/wjh_user_2021_06_16_12_03_15.pcap

#    Timestamp              sPort  dPort  VLAN  sMAC               dMAC               EthType  Src IP:Port  Dst IP:Port  IP Proto  Drop   Severity  Drop reason - Recommended action
                                                                                                                                   Group
---- ---------------------- ------ ------ ----- ------------------ ------------------ -------- ------------ ------------ --------- ------ --------- -----------------------------------------------
1    21/06/16 12:03:12.728  swp1   N/A    N/A   44:38:39:00:a4:84  44:38:39:00:a4:84  IPv4     N/A          N/A          N/A       L2     Error     Source MAC equals destination MAC - Bad packet as received from peer
2    21/06/16 12:03:12.728  swp1   N/A    N/A   44:38:39:00:a4:84  44:38:39:00:a4:84  IPv4     N/A          N/A          N/A       L2     Error     Source MAC equals destination MAC - Bad packet was received from peer
3    21/06/16 12:03:12.745  swp1   N/A    N/A   44:38:39:00:a4:84  44:38:39:00:a4:84  IPv4     N/A          N/A          N/A       L2     Error     Source MAC equals destination MAC - Bad packet was received from peer
4    21/06/16 12:03:12.745  swp1   N/A    N/A   44:38:39:00:a4:84  44:38:39:00:a4:84  IPv4     N/A          N/A          N/A       L2     Error     Source MAC equals destination MAC - Bad packet was received from peer

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